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Namibia's Beatrice Masilingi, who is unable to compete at certain events due to differences in sexual development (DSD), finished first in her 100m semi-final at the World Athletics Under-20s Championships on Wednesday.
Masilingi, 18, is blocked from running distances between 400m and one mile under World Athletics rules.
Earlier she claimed a personal best of 11.20 seconds in the heats in Kenya.
Masilingi was the second quickest qualifier for Friday's final (1430 GMT), running 11.35sec, 0.01sec slower than Jamaican Tina Clayton in another of the three semi-finals.
Fellow Namibian teenager Christine Mboma won silver at the 200m in the Tokyo Olympics earlier this month and is set to race in Friday's heats over the same distance. She is also deemed to have DSD.
Masilingi finished sixth in the 200m final on August 3 in Japan in her first major championships.
It is the same issue that led to South Africa's two-time Olympic 800m champion Caster Semenya being unable to defend her middle-distance crown in Tokyo.